Young children’s estimates of numerosity increase approximately logarithmically with actual set size. The conventional interpretation of this finding is that children’s estimates reflect an innate logarithmic encoding of number. A recent set of findings, however, suggest logarithmic number-line estimates could emerge via a dynamic encoding mechanism that is sensitive to the prior distribution of stimuli. Here we test this idea by examining trial-to-trial changes in logarithmicity of numerosity estimates. Against the dynamic encoding hypothesis, first trial estimates in both adults (Study 1) and adults and children (Study 2) were strongly logarithmic, despite there being zero previous stimuli. Additionally, although numerosity of a previous trial affected adult estimates of numerosity, the nature of this effect varied across experiments, yet always resulted in a logarithmic-to-linear shift from trial-to-trial. These results suggest that a dynamic encoding mechanism is neither necessary nor sufficient to elicit logarithmic estimates of numerosity